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Analyzing the Reaction between Baking Soda and Citric Acid (3 Favorites)

LAB in Solubility, Reaction Rate, Balancing Equations, Stoichiometry. Last updated February 21, 2019.


Summary

In this lab, students will examine the reaction between citric acid and baking soda. They will analyze the chemical equation, balance it and calculate needed quantities of each reactant for a complete reaction. Based on their observations, students will determine if all reactants were completely used during the reaction.

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
  • HS-PS1-7: Use mathematical representation to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Objectives

By the end of this lab, students should be able to

  • Use and apply stoichiometric concepts to determine the ratio of moles in the reaction.
  • Understand solubility rules in order to determine if a reactant is present at the end of a chemical reaction.
  • Determine factors affecting the rates of chemical reactions.

Chemistry Topics

This lab supports students’ understanding of

  • Chemical Reactions
  • Stoichiometry
  • Balancing Equations
  • Rates of Reaction
  • Solubility

Time

Teacher Preparation: 30 minutes

Lesson: 1 hour

Materials

Per lab group:

  • Analytical balance
  • 20g citric acid (H3C6H5O7)
  • 26g baking soda (NaHCO3)
  • Weighing paper or weighing dish
  • 50 mL beaker
  • Deionized water/distilled water
  • 25mL graduated cylinder
  • Periodic Table

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
  • Neutralize any acid spills with baking soda.
  • Wear protective gloves when working with strong acids.

Teacher Notes

  • Students can work in pairs or in a small group of four students during this lab.
  • Citric acid H3C6H5O7 and baking soda NaHCO3 react to form carbon dioxide CO2, water H2O and sodium citrate Na3C6H5O7
  • One mole of citric acid reacts with 3 moles baking soda (sodium bicarbonate) to form 3 moles of carbon dioxide, 3 moles of water and 1 mole of sodium citrate in the following reaction: H3C6H5O7 + 3NaHCO3 à 3CO2 + 3H2O + Na3C6H5O7
  • Prerequisite topics:
    • Solubility
    • Molar mass
    • Balancing equations
    • Chemical reactions
  • Baking soda is partially soluble in water and will have white solids that have not dissolved at the bottom of the beaker in aqueous solution. The reactant citric acid and the product sodium citrate are soluble in aqueous solution. With accurate measurement of the reactants a clear resultant solution affirms that all the baking soda has reacted. A white solid remaining after completion of the reaction indicates the presence of unreacted baking soda.
  • Baking soda and citric acid in solid powder or granular form, as a mixture by observation appears unreactive. Adding water to form an aqueous solution initiates a rapid reaction.
  • Students first respond to the pre-lab questions to determine the ratio of reactants required, how much of the reactants will need to be weighed for the complete reaction using 0.1 mole of citric acid. Students will then weigh each reactant according to the calculated amounts determined from molar mass and the balanced equation. Both weighed reactants are to be placed in the beaker; the students will observe no reaction.
  • Then students will measure 10mL of water and add it to the solid reactants. After the reaction has slowed down students add another 10mL of water to the reaction and swirl until the reaction stops, and there are no remaining solids. The presence of a white precipitate indicates an excess of unreacted baking soda therefore and unbalanced amount of measured reactants.
  • Mixing solid citric acid and baking powder: A chemical reaction is not observable with the naked eye. The reaction is occurring at much slower rate than in aqueous solution.
  • The chemical reaction can be seen with the naked eye when there is a rapid formation of carbon dioxide being produced, with the displacement of liquid.
  • To produce carbon dioxide, the bicarbonate ion needs to come into contact with the acid proton on the citric acid. In the solid state there is very little kinetic energy.
  • In solution, the proton transfer can quickly propagate through the hydrogen bond network in water. The greater kinetic energy in liquid rather than solid form increases the number of molecular collisions, and therefore a significantly more rapid rate of reaction occurs that is observable.

For the Student

Lesson

Background

Baked goods are leavened (to leaven means to raise or make light) with a variety of natural and chemical raising agents. They produce gases that are responsible for the increased volume when a mixture is placed in the oven to bake. Raising agents such as baking soda are responsible for producing and expanding the millions of bubbles trapped in the batter. The reaction is triggered by moisture and or heat. When the batter sets into a firm structure during baking the aeration is preserved, observed as a soft cushion-like texture with miniscule air pockets.

Raising agents also contribute to the taste, texture and color of baked foods. For a successful leavening system, balancing the chemical ingredients minimizes the risk of a bitter flavor, or a too moist or too dry texture. Baking soda requires an acid and moisture to react and neutralize the bitter taste and produce the carbon dioxide air bubbles to lighten the texture.

In this experiment we will use our understanding of chemistry to investigate the reaction between baking soda and citric acid and determine the amount and ratio of each reactant we would need for a complete and balanced reaction.

Objective

To determine the amount of baking soda and citric acid required in a balanced chemical reaction.

Part 1: Prelab Warm-up and Questions

  1. Balance the following equation with reactants of baking soda and citric acid producing carbon dioxide, water and sodium citrate:
___H3C6H5O7 + ___NaHCO3 ___CO2 + ___H2O + ___Na3C6H5O7
  1. Calculate the molar mass for citric acid:
  2. Calculate the molar mass for baking soda:
  3. According to the balanced equation in question 1, for a complete reaction to occur how many grams of each of the reactants would be required?
  4. You will be conducting a lab using 0.1 moles of citric acid. Calculate the mass of citric acid that you would need to weigh:
  5. Based on the ratio of moles: How many moles of baking soda are required to react with 0.1mole of citric acid?
  6. Calculate the number of grams of baking soda required for the lab reaction.

Part 2: Experiment Lab.

Materials

  • Analytical balance
  • Citric acid (H3C6H5O7)
  • Baking soda (NaHCO3)
  • Weighing paper or weighing dish
  • 50 mL beaker
  • Deionized water/distilled water
  • 25mL graduated cylinder

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow teacher instructions for clean-up of materials and disposal of chemicals.
  • Immediately alert your teacher if any solution gets on your skin, and thoroughly flush their skin with water.
  • Wear protective gloves when working with strong acids.

Procedure

Use your Pre-lab data and the following recording space at each step as you go through the procedures.

  1. Use weighing paper and the analytical balance to measure the required amount of citric acid Prelab Question 6 and baking powder Prelab Question 7. Place them both into the beaker. Write down your observation of this mixture:
  2. Measure 10mL of water and gently pour it into the beaker with citric acid and baking soda. Write down your observation:
  3. Measure an additional 10mL quantity of water and gently pour it into the beaker with citric acid and baking soda. Write down your observation:
  4. Between 1-2 minutes later add another 10mL of water and swirl the beaker. Write down your observation:
  5. Place the beaker on the lab table until there is no further observable reaction. Describe the remaining liquid:
  6. Explain the result of your remaining liquid:
  7. You are assigned to bake a cake for a celebratory event and are tasked with finding a recipe that is most likely to create a moist and light (well raised) cake texture. Outline some of the key factors you will be analyzing when making your recipe selection, with evidence and reasoning.

Section 3: Analysis

  1. Review your observation of Procedure step 1. Explain this in terms of the chemical reaction taking place.
  2. Was the quantity of reactants used in this experiment balanced according to the theoretical equation? Explain why or why not.
  3. If an additional 10mL of water was added in the reaction, what would you hypothesize would happen? Explain your reasoning.